致密油藏不同微观孔隙结构储层CO2驱动用特征及影响因素

致密砂岩储层微观孔隙结构对CO₂驱油特征有重大影响。基于铸体薄片分析、扫描电镜、高压压汞和核磁共振测试等实验结果，建立了姬塬油田长8油层组微观孔隙结构分类标准，并选取每种类型储层有代表性的岩心样品开展不同驱替压力下的CO₂驱油实验，辅以核磁共振T₂谱，对3种类型孔隙结构储层在不同驱替压力下大、小孔隙中的原油动用特征进行了研究，详细分析了储层物性、孔隙结构和黏土矿物对CO₂驱油效率的影响。结果表明：研究区长8油层组的孔隙结构可以划分为Ⅰ、Ⅱ、Ⅲ类，3种类型孔隙结构对应的储集空间和渗流能力依次下降。Ⅱ类储层CO₂混相驱油效率最大，Ⅲ类储层CO₂非混相驱油效率最大；不同孔径孔喉中原油的动用特征随驱替压力和储层孔隙结构类型的不同而存在较大差异。CO₂非混相驱油效率与岩石渗透率、孔喉半径、分选系数和黏土矿物含量存在较好的相关性，而CO₂混相驱油效率的高低与孔隙结构参数和黏土矿物含量有关。Ⅱ类储层作为未来主要挖潜层位更适合开展注CO₂驱。

Characteristics and influencing factors of CO2 flooding in different microscopic pore structures in tight reservoirs

The microscopic pore structures of tight sandstone reservoirs have a significant impact on the CO₂ flooding characteristics. Based on the experimental results from thin section analysis, SEM, high-pressure mercury injection and NMR testing, this paper establishes a classification standard for the microscopic pore structures of the Chang 8 oil-bearing formation in Jiyuan oilfield, carries out CO₂ flooding experiment under different displacement pressures using the representative core samples of each type of reservoir, and in combination with NMR T₂ spectroscopy, studies the displacement characteristics of crude oil in macro and small pores under various displacement pressures in reservoirs of 3 types of pore structures, and detailedly analyzes the effect of reservoir physical property, pore structure and clay minerals on CO₂ flooding efficiency. The results show that the pore structure of Chang 8 reservoir in the study area can be divided into type I, Ⅱ and Ⅲ. The reservoir space and percolation ability corresponding to the three types of pore structures decrease successively. Type Ⅱ reservoir has the largest miscible CO₂ flooding efficiency, and type Ⅲ reservoir has the largest immiscible CO₂ flooding efficiency; the displacement characteristics of crude oil in pore throats with different pore sizes vary greatly with different displacement pressure and various types of reservoir pore structures. Immiscible CO₂ flooding efficiency has a good correlation with rock permeability, pore throat radius, sorting coefficient and clay mineral content, while the level of miscible CO₂ flooding efficiency is related to pore structure parameters and clay mineral content. As the main production potential tapping horizon in the future, type Ⅱ reservoir is more suitable for CO₂ flooding. These achievements provide a method and basis for the reasonable and efficient CO₂ flooding of Chang 8 reservoir in Jiyuan oilfield.